1. Field of the Invention
The present invention relates to a reduction gear capable of reducing so-called rattle noises and a frictional load application (or generation) member for the reduction gear.
2. Description of the Related Art
In a mechanical reduction gear, a “play” is provided between gears. The play is indispensable for smooth rotation of the gears. However, there is a problem that the presence of a play induces so-called “rattle noises” in operation under a small load.
The rattle noise designates a noise generated by the repeated contact and separation between the tooth surface of a driving-side gear and the tooth surface of a driven-side gear due to the vibration or pulsation of a motor, a variation in load on the driven object side, or the like.
In order to reduce such rattle noises, for example, Japanese Patent Laid-Open Publication No. 2002-115754 discloses a structure for applying a light frictional load to a gear shaft. If a frictional load is applied to the gear shaft, the tooth surface of a driven-side gear is unlikely to be separated from the tooth surface of a driving-side gear. Therefore, the generation of rattle noises can be more reduced.
In the above-mentioned Japanese Patent Laid-Open Publication No. 2002-115754, for example, the structure as shown in FIG. 5(A) or 5(B) has been proposed so as to apply (or generate) a frictional load to the gear shaft.
In the structure shown in FIG. 5(A), a bearing housing 14 housing a bearing 12 of an intermediate shaft 10 therein is extended toward the interior of a gear case 16 to form an extended part 14a. An oil seal 20 for applying a frictional load is interposed between the extended part 14a and the intermediate shaft 10. The extended part 14a has a larger diameter than that of a part of the bearing housing 14, in which the bearing 12 is housed, so as to house the oil seal 20 therein.
In the structure shown in FIG. 5(B), a part of a bearing housing 30 of the bearing 12 is extended toward the gear case 16 to form an extended part 30A. An O-ring 32 for generating a frictional load is housed in the inner space of the extended part 30A.
In the above-described structure shown in FIG. 5(A), however, the extended part 14a of the bearing housing 14, which has a larger diameter, is extended beyond the bearing 12 toward the gear. Therefore, there is a problem that positional interference with another gear is likely to be caused. In particular, if a number of gears are present in the gear case 16 as in the case of a multistage reduction gear, it is often difficult to ensure a space where the oil seal 20 for generating a frictional load is to be provided. The design of increasing the axial length of the gear case 16 for the placement of the oil seal 20 for applying a frictional load is normally unacceptable.
The structure shown in FIG. 5(B) has also a problem that a space is difficult to be ensured if the size is small. Therefore, it is sometimes difficult to house the O-ring 32 of desired size. Moreover, the O-ring 32 is not axially positioned yet to be simply housed between the bearing 12 and the bearing housing 30. Therefore, a thrust load with the deformation of the O-ring 32 may possibly affect an inner ring 12A. If the bearing 12 rotates while an axial load is being applied only to its inner ring 12A, smooth relative rotation between the inner ring and the outer ring is inhibited, inevitably inducing a reduction of lifetime.
In order to ensure that the bearing 12 does not suffer from the axial effects of the O-ring 32, it is necessary to provide a positioning part (a thrust load supporting part) exclusively for the O-ring 32 between the O-ring 32 and the bearing 12. As a result, the structure is more complicated. In addition, the axial length of the gear case 16 is increased in some cases.